Pyrido[4,3,2-kl]acridines represent a new class of heterocycles, isomers of marine alkaloids. The 7H-pyrido[4,3,2-kl]acridine reacts as an electron rich heterocycle, and in particular via electrophilic substitution such as H/D exchange and the Vilsmeier-Haack reaction. The reaction is fully regioselective and gives the corresponding 6-substituted derivatives. The pyrido[4,3,2-kl]acridin-4-one reacts with amines and thiol, via 1,4-Michael addition to give the 6-amino or 6-thio analogues in a very efficient way. Molecular calculations account for the observed regioselectivity.